1. Field of the Invention
This invention relates to a multitrack audio system, more particularly to a multitrack audio system having a rotary drum head for recording/playback audio signals which are sampled by using a plurality of specified sampling frequencies, such as 31.5 kHz, 63 kHz, 94.5 kHz, and 189 kHz, and then modulated into digital signals.
2. Description of the Prior Art
As one of applications of 8-mm video system, it is well known that a 8-mm video pulse code modulation (PCM) multitrack audio system for recording PCM audio signals into video tracks has been developed.
In the PCM multi track system, a video signal area of 180 deg as a relation betwen a head of the 8-mm video and magnetic tape shown in FIG. 1 is divided into 5 areas of 36 deg each as shown in FIG. 2. PCM audio signals are recorded into the 5 areas. Namely, the audio signals are recorded into all 6 tracks as shown in FIG. 3.
In this case, the audio signals per 1/60 seconds are recorded into one field which is made of 6 tracks. The field is made of, as shown in FIG. 4, 132 blocks (block #0 to block #131) which comprises a synchronization code (3 bits), an address code (8 bits), a Q parity code (8 bits), a data (4 data.times.8 bits), a P parity code (8 bits), a data (4 data .times.8 bits), and a CRC code (16 bits). Moreover, in the PCM multitrack system, the audio signals are sampled by the sampling frequency of 31.5 kHz for recording and then converted into PCM digital signals and then recorded onto the magnetic tape. In this case, a frequency band becomes about 15 kHz in half of the sampling frequency.
By the way, they say that it is difficult to hear sound over 20 kHz audiability by mankind. As mentioned above, it is adequate to use frequencies up to about 15 kHz for practical applications.
Sound is transmitted to the brain through the skin near ears and the skeletons of inner ears, thereby it is known that .alpha.-waves are increased in the brain of a person by hearing the sound of supersonic waves over 20 kHz.
In the conventional PCM multitrack system, for example the frequency range of about 15 kHz can be recorded and played back by using the sampling frequency of 31.5 kHz.
While, it is desired to use audio signals up to 30 kHz (twice of the frequency range of 15 kHz), 45 kHz, or 90 kHz (twice of the frequency range of 45 kHz) for increasing .alpha.-wave in the brain of a person.